Diorganomagnesium compounds are well known for their usefulness in a wide variety of chemical reactions. As reagents, these compounds can be used for the reduction of ketones, the metalation of aromatic compounds and the alkylation of metal halides or oxides to the corresponding metal alkyls. While they perform many of the same types of functions performed by Grignard reagents, diorganomagnesium compounds, owing to differences in electronic and steric factors, are more reactive than Grignard reagents towards certain types of compounds. Some of their uses are disclosed in Kamienski et al., U.S. Pat. No. 3,646,231, Feb. 29, 1972, and Kamienski et al., U.S. Pat. No. 3,822,219, July 2, 1974. As catalysts, diorganomagnesium compounds are useful in the dimerization and polymerization of olefins (Stamicarbon, British Pat. No. 1,251,177, Oct. 27, 1971), the polymerization of epoxides (Ito et al., U.S. Pat. No. 3,444,102, May 13, 1969), and the preparation of telomers (Kamienski et al., U.S. Pat. No. 3,742,077, June 26, 1973).
The utility of diorganomagnesium compounds is lessened by the fact that many are either solids or highly viscous liquids and all are unstable upon exposure to moisture and air. This problem is generally overcome either by dissolving the compound in an inert hydrocarbon solvent or by solvating the compound and keeping it under an inert atmosphere. Many diorganomagnesium compounds, particularly those with straight-chain lower alkyl groups with a chain length of up to 4 carbon atoms, are insoluble by themselves in hydrocarbon solvents and thus require solubilizing agents which will form a soluble complex. Examples of such solubilizing agents are alkyllithium compounds (Kamienski et al., U.S. Pat. No. 3,742,077, June 26, 1973), dialkyl zinc compounds (Ito et al., U.S. Pat. No. 3,444,102, May 13, 1969), alkali metal hydrides (Ashby, U.S. Pat. No. 3,655,790, Apr. 11, 1972), and organoaluminum compounds (deVries, U.S. Pat. No. 3,737,393, June 5, 1973, and Kobetz et al., U.S. Pat. No. 3,028,319, Apr. 3, 1962).
Solvation involves the use of an ether or an organic base molecule in direct association with the magnesium atom. Although the resulting complex is liquid in form, it is unfavorable in terms of reactivity, since the ether or base molecule inhibits the effectiveness of the organomagnesium compound, particularly when the latter is used as a Ziegler-type catalyst. The use of ether is particularly undesirable due to considerations of flammability and explosibility, and because it introduces soluble alkyl magnesium halide according to the equilibrium of Schlenk, Berichte der Deutschen Chemischen Gesselschaft, Vol. 64, p. 734 (1931), by promoting the reaction EQU R.sub.2 Mg+MgX.sub.2 .revreaction.2RMgX
where R is alkyl and X is halogen.
Solubilization also serves to enhance the reaction rate and facilitate handling and transferring by reducing the viscosity of reaction mixtures. Although similar results have been achieved by the use of chloroaryl solvents to form low viscosity suspensions of the insoluble compounds, as described in Nudenberg et al., U.S. Pat. No. 3,264,360, Aug. 2, 1966, the results are more effective with a homogeneous mixture.
Solubilization also facilitates the preparation of organomagnesium compounds, since those which are insoluble are difficult to prepare in a form free of undesirable halides. The preparation of soluble organomagnesium compounds by direct reaction of magnesium metal with an alkyl halide is disclosed in Glaze and Selman, Journal of Organometallic Chemistry, Vol. 5, p. 477 (1967), and W. N. Smith, Journal of Organometallic Chemistry, Vol. 64, p. 25 (1974), where the alkyl halide contains a minimum of 5 carbon atoms. Since the products made from such starting materials are inherently hydrocarbon-soluble, they are readily separable from the concurrently produced magnesium halide and whatever unreacted magnesium remains. When straight-chain alkyls of less than 5 carbon atoms in length are used, however, the product remains as a solid in the slurry formed by the solvent, the magnesium halide, and the unreacted magnesium, since the product itself is insoluble in the solvent. This process thus requires a solubilizing agent to make recovery of the product possible when lower alkyl halides are used. Lower alkyl organomagnesium compounds are particularly desirable as reagents and catalysts owing to their relatively high magnesium content on a weight basis.
Other methods of preparation include the mercury-magnesium exchange method, as disclosed in Cowan and Mosher, Journal of Organic Chemistry, Vol. 27, p. 1 (1962), and the dioxanate-precipitation method as disclosed in Schlenk, supra. The mercury method, EQU R.sub.2 Hg+Mg.fwdarw.R.sub.2 Mg+Hg
where R is alkyl, is limited by the high cost of dialkylmercury compounds, and the health hazards involved in their use. The reaction itself is hazardous since it proceeds rapidly and exothermically after an inhibition period.
The dioxanate-precipitation method, ##STR1## where R is alkyl and X is halogen, involves removal of magnesium halide from ether solutions of Grignard reagents by precipitation of a complex which the dioxane forms with the halide. This is a tedious process and results in an etherated dialkylmagnesium complex from which the ether must be removed prior to use of the dialkylmagnesium as a catalyst.
Dialkylmagnesiums can also be prepared from alkyllithiums, as described in Kamienski et al., U.S. Pat. No. 3,646,231, Feb. 29, 1972, by precipitation of lithium halide, EQU MgX.sub.2 +2RLi.fwdarw.R.sub.2 Mg+2LiX
where R is alkyl and X is halogen. As in the Glaze and Selman method described above, this process is unsuitable for straight-chain lower alkyl diorganomagnesiums which are insoluble in hydrocarbon solvents, since separation of the diorganomagnesium from the product mixture is impossible. The use of basic solvents renders separation possible but requires subsequent desolvation.
It is therefore an object of the present invention to provide a hydrocarbon-soluble diorganomagnesium composition of high magnesium content.
A further object of the present invention is to provide a process by which hydrocarbon-soluble diorganomagnesium compositions of high magnesium content can be prepared by the direct reaction of alkyl halides with magnesium.
A still further object of the present invention is to provide a means for solubilizing straight-chain lower alkyl diorganomagnesium compounds in hydrocarbon solvents.
Further objects will be apparent from the following description.